1. Field of the Invention
The present invention relates to a filter module, and in particular an EMC-/EMI-filter module contained in a dual-in-line package.
2. Description of the Prior Art
In the design of branched individual networks of data and signal processing blocks, the use of symmetrical systems is increasingly regarded as a particularly suitable design basis. The ever increasing cost considerations in connection with such systems generally prohibit the use of a screened line control, particularly in the systems requiring a large number of terminals or measuring and positioning circuitry and the extensive cabling associated therewith. In order to cut the high costs of such systems, one would ideally utilize unscreened multi-wire lines of telephone, teleprinter or telex networks which are simple to install for data and signal lines up to several hundred thousand bits per second.
The use of such unscreened multi-wire lines presents two problems which must be overcome before such lines can be used with reliable results in most symmetrical systems. First, the line must have electromagnetic compatibility (EMC), i.e., the unscreened, electrically open system cannot be influenced by stray electromagnetic interference fields. Second, the lines must also exhibit radio interference suppression (EMI), i.e., the system or line itself can be permitted to emit high frequency electromagnetic energy at 10 kHz only within the legally permitted levels.
A particularly suitable filter for achieving the above ends is described in Siemens publication 51 (1977), Volume 8, page 621. The circuit consists basically of a number of matched LC filters utilizing a quadruple choke. This filter provides an interface between the line and the processing apparatus which matches in a highly symmetrical fashion the respective signal outputs and inputs to the lines. The particular filter described in the publication is designed for use with two symmetrical signal circuits.